In the disclosure of the present invention reference is mostly made to the treatment of diabetes by injection or infusion of insulin, however, this is only an exemplary use of the present invention.
Portable drug delivery devices for delivering a drug to a patient are well known and generally comprise a reservoir adapted to contain a liquid drug and having an outlet in fluid communication with a hollow infusion needle, as well as expelling means for expelling a drug out of the reservoir and through the skin of the subject via the hollow needle. Such devices are often termed infusion pumps.
Basically, infusion pumps can be divided into two classes. The first class comprises infusion pumps which are relatively expensive pumps intended for 3-4 years use, for which reason the initial cost for such a pump often is a barrier to this type of therapy. Although more complex than traditional syringes and pens, the pump offer the advantages of continuous infusion of insulin, precision in dosing and optionally programmable delivery profiles and user actuated bolus infusions in connections with meals.
Addressing the above problem, several attempts have been made to provide a second class of drug infusion devices that are low in cost and convenient to use. Some of these devices are intended to be partially or entirely disposable and may provide many of the advantages associated with an infusion pump without the attendant cost and inconveniences, e.g. the pump may be prefilled thus avoiding the need for filling or refilling a drug reservoir. Examples of this type of infusion devices are known from U.S. Pat. Nos. 4,340,048 and 4,552,561 (based on osmotic pumps), U.S. Pat. No. 5,858,001 (based on a piston pump), U.S. Pat. No. 6,280,148 (based on a membrane pump), U.S. Pat. No. 5,957,895 (based on a flow restrictor pump (also know as a bleeding hole pump)), U.S. Pat. No. 5,527,288 (based on a gas generating pump), or U.S. Pat. No. 5,814,020 (based on a swellable gel) which all in the last decades have been proposed for use in inexpensive, primarily disposable drug infusion devices, the cited documents being incorporated by reference. U.S. Pat. No. 6,364,865 discloses a manually held infusion device allowing two vial-type containers to be connected and a pressure to be build up in one of the containers to thereby expel a drug contained in that container.
The disposable pumps generally comprises a skin-contacting mounting surface adapted for application to the skin of a subject by adhesive means, and with the infusion needle arranged such that in a situation of use it projects from the mounting surface to thereby penetrate the skin of the subject, whereby the place where the needle penetrates the skin is covered while the appliance is in use. The infusion needle may be arranged to permanently project from the mounting surface such that the needle is inserted simultaneously with the application of the infusion pump, this as disclosed in U.S. Pat. Nos. 2,605,765, 4,340,048 and in EP 1 177 802, or the needle may be supplied with the device in a retracted state, i.e. with the distal pointed end of the needle “hidden” inside the pump device, this allowing the user to place the pump device on the skin without the possibility of observing the needle, this as disclosed in U.S. Pat. Nos. 5,858,001 and 5,814,020.
As an alternative to a needle, a cannula in combination with an insertion needle which is withdrawn after insertion thereof may be used. Typically, the cannula is in the form of a relatively soft infusion cannula (e.g. a Teflon® cannula) and a there through arranged removable insertion needle. This type of cannula and needle arrangement is well known from so-called infusion sets, such infusion sets typically being used to provide an infusion site in combination with (durable) infusion pumps. However, recently a disposable pump has been disclosed comprising an insertable soft cannula in combination with an insertion needle. More specifically, WO 03/090509 shows a skin mountable drug delivery device comprising an initially concealed soft cannula through which an insertion needle is arranged. With the device mounted on a skin surface the cannula can be released and inserted angled through the skin, the pointed distal end of the insertion needle projecting from the distal end of the cannula. When the cannula is fully inserted the insertion needle is withdrawn.
When a transcutaneous device, e.g. a soft cannula or a sensor, is introduced normally an insertion needle is used in combination therewith in order to provide a skin piercing distal end as well as support and/or protect the transcutaneous device during insertion. After insertion the needle is retracted, either manually or automatically, and is either removed from the medical device or retracted into it. An insertion needle may be arranged either co-axially with the transcutaneous device or in parallel therewith as long it is secured that the two members will be held together during insertion. As appears, the use of an introduction needle normally adds to the complexity of a medical, both in user-friendliness, size and cost.